TO-UNDO: switch to junit-benchmark 0.8.0-SNAPSHOT

There is a problem with the junit-benchmark: it includes the @Before and
@After methods in the timings:
http://issues.carrot2.org/browse/JUNITBENCH-54

The recommended solution -- uglifying the code as to be unreadable,
demonstrated here:
https://github.com/carrotsearch/junit-benchmarks/blob/be41b475/src/test/java/com/carrotsearch/junitbenchmarks/TestJUnitHooksWorkAround.java#L20
-- was not acceptable to this developer, who therefore implemented a
workaround relieving junit-benchmark users of the need for ugly @Rule
incantations: https://github.com/carrotsearch/junit-benchmarks/pull/14

For the moment, let's use junit-benchmark version 0.8.0-SNAPSHOT for
that reason, with the understanding that the developers need to compile
the version from that pull request locally until a more final solution
is found.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Turn AddOpBenchmark into a JUnit Benchmark

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Turn the MapperBenchmark into a JUnit Benchmark

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>